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CHAPTER 3 Ecosystems: What are they and how do they work?
Unit 1 Test Summary: Chapters 1/2/25
Some Ecosystems Produce Plant Matter Faster Than Others Do Gross primary productivity (GPP) Rate at which an ecosystem’s producers convert solar energy to chemical energy and biomass Kcal/m 2 /year Net primary productivity (NPP) Rate at which an ecosystem’s producers convert solar energy to chemical energy, minus the rate at which producers use energy for aerobic respiration Ecosystems and life zones differ in their NPP.
Estimated Annual Average NPP in Major Life Zones and Ecosystems Fig. 3-15, p. 66
Forest Ecosystem Observation What living (biotic) and non-living (abiotic) components can you observe or infer in this forested ecosystem? [List them.] Be as specific as possible. For each biotic component, is it a producer (“autotroph”; makes nutrients it needs from energy and compounds from its environment) or a consumer (“heterotroph”; must obtain its energy-storing molecules and other nutrients by feeding on other organisms)? For consumers, which type is it? primary consumer (herbivore) secondary consumer carnivore which feeds on the flesh of herbivores tertiary (higher-level) consumer which feeds on flesh of other carnivores. decomposer omnivore
Forest Ecosystem Observation, cont. Write about the vertical spatial arrangement (i.e. stratification) of the plants. What types of plants dominate the various strata? Sketch a diagram of the stratification, labeling your sketch. Identify as many of the plant species as you can. (e.g., white oak)
Forest Ecosystem Observation, cont. Write a nature haiku, a short poem usually written in three lines. Don’t worry about syllables.
Producer, Consumer, Decomposer, or Detritivore?
Teeth! Herbivores have lots of molars—back, flat teeth for grinding branches, grasses and seeds. Since their food doesn’t try to escape, they use their front teeth like pruning sheers to clip leaves and stems.
Teeth! Carnivore teeth on the other hand, are sharp and scissor-like. Their front teeth bite and hold on while their long canine teeth tear into prey. Their molars are used for slicing rather than chewing because they mainly swallow their food in whole chunks.
Teeth! Omnivores, such as otters and bears, eat both plants and meat, so not surprisingly, they have a combination of sharp front teeth and grinding molars. Humans are set up with teeth like this, whether we eat meat or not, so look in your own mouth to see an example of omnivore teeth.
Core Case Study: Tropical Rain Forests Are Disappearing Cover about 2% of the earth’s land surface Contain about 50% of the world’s known plant and animal species Disruption will have three major harmful effects Reduce biodiversity Accelerate global warming Change regional weather patterns
Natural Capital Degradation: Satellite Image of the Loss of Tropical Rain Forest Fig. 3-1a, p. 54
Question What did we learn yesterday that can explain why the earth could support more people if they all ate at lower trophic levels by consuming grains, vegetables, and fruits directly rather than passing such crops through another trophic level and eating grain eaters or herbivores such as cattle?
Purchase Knob Trip Monday, 9.22 The study of nature’s calendar.
Purchase Knob Follow-Up: Handout
NY Times Article--Salamaders on-the-cusp-of-climate-change
3-4 What Happens to Matter in an Ecosystem? Concept 3-4 Matter, in the form of nutrients, cycles within and among ecosystems and the biosphere, and human activities are altering these chemical cycles.
Biogeochemical Cycles What does this word mean? Handout/Webquest Water (Hydrological) Cycle How are humans impacting the water cycle? Carbon Cycle Ocean Acidification Nitrogen Cycle 5: Name three ways humans have impacted the nitrogen cycle. Discuss Phosphorous Cycle
Teams—How are humans impacting the following biogeochemical cycles? What are the potential or realized implications? Hydrological Carbon Nitrogen Phosphorous Sulfur
Water Cycles through the Biosphere Natural renewal of water quality: three major processes Evaporation Precipitation Transpiration Alteration of the hydrologic cycle by humans Withdrawal of large amounts of freshwater at rates faster than nature can replace it Clearing vegetation Increased flooding when wetlands are drained
Hydrologic Cycle Including Harmful Impacts of Human Activities Fig. 3-16, p. 67
Carbon Cycle Depends on Photosynthesis and Respiration Link between photosynthesis in producers and respiration in producers, consumers, and decomposers Additional CO 2 added to the atmosphere Tree clearing Burning of fossil fuels Warms the atmosphere
Natural Capital: Carbon Cycle with Major Harmful Impacts of Human Activities Fig. 3-19, p. 70
Increase in Atmospheric Carbon Dioxide, Supplement 9, Fig 14
Nitrogen Cycle Figure 1: The nitrogen cycle. Yellow arrows indicate human sources of nitrogen to the environment. Red arrows indicate processes in which microorganisms participate in the transformation of nitrogen. Blue arrows indicate physical forces acting on nitrogen. And green arrows indicate natural processes affecting the form and fate of nitrogen that do not involve microbes.
Nitrogen Cycles through the Biosphere: Bacteria in Action (1) Nitrogen fixed by lightning Nitrogen fixed by bacteria and cyanobacteria Combine gaseous nitrogen with hydrogen to make ammonia (NH 3 ) and ammonium ions (NH 4 + ) Nitrification Soil bacteria change ammonia and ammonium ions to nitrate ions (NO 3 - ) Denitrification Nitrate ions back to nitrogen gas
Nitrogen Cycles through the Biosphere: Bacteria in Action (2) Human intervention in the nitrogen cycle 1.Additional NO and N 2 O in atmosphere from burning fossil fuels; also causes acid rain 2.N 2 O to atmosphere from bacteria acting on fertilizers and manure 3.Destruction of forest, grasslands, and wetlands 4.Add excess nitrates to bodies of water 5.Remove nitrogen from topsoil
Nitrogen Cycle in a Terrestrial Ecosystem with Major Harmful Human Impacts Fig. 3-20, p. 71
Human Input of Nitrogen into the Environment Supplement 9, Fig 16
Nitrogen Fixation N 2 NH 4 + Nitrogen fixation is the process wherein N 2 is converted to ammonium, or NH 4 +. This is the only way that organisms can attain nitrogen directly from the atmosphere; the few that can do this are called nitrogen fixing organisms. Certain bacteria, including those among the genus Rhizobium, are able to fix nitrogen (or convert it to ammonium) through metabolic processes, analogous to the way mammals convert oxygen to CO2 when they breathe. Nitrogen fixing bacteria often form symbiotic relationships with host plants. This symbiosis is well-known to occur in the legume family of plants (e.g., beans, peas, and clover). In this relationship, nitrogen fixing bacteria inhabit legume root nodules (Figure 2) and receive carbohydrates and a favorable environment from their host plant in exchange for some of the nitrogen they fix. There are also nitrogen fixing bacteria that exist without plant hosts, known as free-living nitrogen fixers. In aquatic environments, blue-green algae (really a bacteria called cyanobacteria) are an important free- living nitrogen fixer. organismsgenus symbiosis aquatic In addition to nitrogen fixing bacteria, high-energy natural events such as lightning, forest fires, and even hot lava flows can cause the fixation of smaller, but significant, amounts of nitrogen. The high energy of these natural phenomena can break the triple bonds of N 2 molecules, thereby making individual N atoms available for chemical transformation.energymoleculesatoms Within the last century, humans have become as important a source of fixed nitrogen as all natural sources combined. Burning fossil fuels, using synthetic nitrogen fertilizers, and cultivation of legumes all fix nitrogen. Through these activities, humans have more than doubled the amount of fixed nitrogen that is pumped into the biosphere every year (Figure 3), the consequences of which are discussed below.biosphere
Denitrification Denitrification is an anaerobic process that is carried out by denitrifying bacteria, which convert nitrate to dinitrogen in the following sequence: Nitric oxide and nitrous oxide are gases that have environmental impacts. Nitric oxide (NO) contributes to smog, and nitrous oxide (N 2 O) is an important greenhouse gas, thereby contributing to global climate change.smog greenhouse gas
Nitrification Some of the ammonium produced by decomposition is converted to nitrate (NO 3 - ) via a process called nitrification. The process of nitrification has some important consequences. Ammonium ions (NH 4 + ) are positively charged and therefore stick (are sorbed) to negatively charged clay particles and soil organic matter. The positive charge prevents ammonium nitrogen from being washed out of the soil (or leached) by rainfall. In contrast, the negatively charged nitrate ion is not held by soil particles and so can be washed out of the soil, leading to decreased soil fertility and nitrate enrichment of downstream surface and groundwater.nitrificationionsgroundwater Leaching Note that some of the nitrates produced are taken up by plants.
Nitrogen Mineralization Conversion of organic forms of N (e.g., proteins, DNA) to inorganic forms (ammonium), which is available to plants. Decomposers
How have humans impacted the nitrogen cycle?
The Phosphorous Cycle A SOIL-BASED VIEW OF THE PHOSPHORUS CYCLE Initially, phosphate weathers from rocks. The small losses in a terrestrial system caused by leaching through the action of rain are balanced in the gains from weathering rocks. In soil, phosphate is absorbed on clay surfaces and organic matter particles and becomes incorporated (immobilized). Plants dissolve ionized forms of phosphate. Herbivores obtain phosphorus by eating plants, and carnivores by eating herbivores. Herbivores and carnivores excrete phosphorus as a waste product in urine and feces. Phosphorus is released back to the soil when plants or animal matter decomposes and the cycle repeats. A GLOBAL VIEW OF THE PHOSPHORUS CYCLE The phosphorus cycle occurs when phosphorus moves from land to sediments in the seas and then back to land again. The main storage for phosphorus is in the earth’s crust. On land phosphorus is usually found in the form of phosphates. By the process of weathering and erosion phosphates enter rivers and streams that transport them to the ocean. Once in the ocean the phosphorus accumulates on continental shelves in the form of insoluble deposits. After millions of years, the crustal plates rise from the sea floor and expose the phosphates on land. After more time, weathering will release them from rock and the cycle's geochemical phase begins again.
Phosphorus Cycles through the Biosphere Cycles through water, the earth’s crust, and living organisms Most of these compounds contain phosphate ions (PO 4 3- ) Limiting factor for plant growth Impact of human activities: 1.Clearing forests 2.Removing large amounts of phosphate from the earth to make fertilizers 3.Erosion leaches phosphates into streams
Phosphorus Cycle with Major Harmful Human Impacts Fig. 3-21, p. 73
Sulfur Cycles through the Biosphere Sulfur is found in organisms, ocean sediments, soil, rocks, and fossil fuels. Human activities affect the sulfur cycle: Burn sulfur-containing coal and oil Refine sulfur-containing petroleum to make gasoline, heating oil, etc. Convert sulfur-containing metallic mineral ores Once the sulfur is in the atmosphere, SO 2 is converted to droplets of sulfuric acid (H 2 SO 4 ) and particles of sulfate (SO 4 2- ) salts, which return to the earth as acid deposition.
Natural Capital: Sulfur Cycle with Major Harmful Impacts of Human Activities Fig. 3-22, p. 74